Weird behavior power supply Total Recall

[Zerro]

I believe that this power branche is ok. BTW if power feed at input is about 20V, at stabil is lost 5V, to get 15V. With current 40mA at stabil, those 5V will give 200mW of junk power lost in heat at stabil. Good cooler will make it up. Important is that this stabil will eat some power drop, to work properly, so you must put at input something more than outpot voltage. 20V is ok. Higher voltage drop at input-output at stabil - higher junk heat.

[Ricotjuh]

Yes, I also believe that the power supply is fine now. I also have a stable -15.14V after my 7915. So that's good.
But I've added a video, and there you can see why I still have my doubts. As an example I measure here on pin 3 of the MN3005. Now according to the manual I should measure -9.71V. But as can be seen in the video, it is not stable. This also applies to some other voltages.

https://youtu.be/f6O5aHMeq9Y

[jimilee]

Everything looks correct. Is the effect no working properly? I believe that one has a bipolar cap, doesn't it?


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[Ricotjuh]

Everything looks correct. Is the effect no working properly? I believe that one has a bipolar cap, doesn't it?


Sent from my iPhone using Tapatalk

Yes, it has a bipolar capacitor in it. C35, 2.2uF and and is in the feedback loop of IC9_B.
I have not tested the pedal yet. I want everything to be set up correctly first. So you still have to set trimmers. I wanted to do this with a function generator and oscilloscope. But unfortunately I can't find any instructions for this on Madbean. I found the link to David Morrin on how to calibrate the EH 7850. However, I don't think that description is entirely clear.
So, does anyone here have a step-by-step description of how to set up the trimmers with the oscilloscope?


Edit:
Just trying to calibrate with an audio probe. Followed instructions as stated in the manual. Then connect audio probe to either pin3 or pin4 or IC6. Then I hear a continuous high-pitched beep. When I measure this with my oscilloscope, I see the following picture. Clock signals look good. There is no signal at the input. But I do see a signal around 8.6 kHz. (On pin 4 this is also the same but I see that my measuring cursor is not in the right position, so it does not measure the full period here)
Pin 3 and 4 do differ in amplitude. I should only measure my delayed signal here, right? In this case I shouldn't measure anything as I have no input connected.

Also tested with input signal. Then I indeed hear a delayed signal on pins 3 and 4. But the high frequency predominates.
Please your expertise.

[thomasha]

Depending what you are trying to achieve you need to have a signal or not.

To bias the BBD use a sine wave, increase the gain so that the wave distorts in the BBD and adjust the bias so that the wave is roughly symmetric. This depends on the delay setting, so either choose your preferred setting or set it with the pot half-way. You want to have the same headroom on both sides, using the distorted wave helps, because it definitely uses all the headroom available. The clock noise right after the BBD is normal. I prefer to measure at the input of the opamp, so that it is away enough from the output and some of the noise is gone. Do the same for the second BBD.

The gain between BBDs should be adjusted so that the second BBD sees the same voltage as the first.

To adjust the balance at the output of the second BBD I do it without signal. You will see the clock noise and you can minimize it by adjusting the trimmer. I am such a fan of this thing, that in my build I added  a trimmer right after the first BBD too. I don't think it helped though, the noise level seems to be the same.

The gain stage after the second BBD is adjusted so that you have unity gain between the two sides of the compander, if I am not mistaken.
It is basically summarized here, although here you have different BBDs. You will have to try different delay settings until you find one where most of the delay time is usable. For the noise balance, the highest delay time is suggested, since everything above 20k is not audible anyway.

[Ricotjuh]

Just took a measurement. I still had a BBD Probe from D_H. So I did the measurements with that.
Output signal from the first BBD.


Measured at the same point but raised the amplitude of the input signal. Here it can be seen that the signal is starting to clip. With BIAS 1 adjusted in such a way that it is cut off equally on both sides.


The same point here, but with an even higher overload.


The following points were measured after the second BBD. Same procedures here too.
Here's a clean signal on the output.


Slightly distorted here.


And here it is again distorted. But still neatly symmetrical.


So I think the bias adjustment is done right?!
Then there are the gain settings. This seems to go well for the first stage. Here I get amplification set to 1x between pin 7 of ic6 and pin 7 of ic7 by means of trimmer Gain 1.
But then Gain 2. So when I go through the next step: "Connect your audio probe to pin1 of IC4_A. Adjust the GAIN2
trimmer until the output is the same or slightly above the volume input of pin7 on IC6." Then here's a difference. Where I measure 3.28V on pin 7 of ic 6 and 1.28V on pin 1 of ic 4.
But when I measure between the NE570 compander on pin 7 and on pin 14, I get it properly adjusted to a gain of 1x by means of the Gain 2 trimmer.
Which of the above methods is correct?

[thomasha]

Hi,

Bias seems OK.

According to Howard Davies for the EH7850: "TRIM 5 (GAIN 2):  Unity between NE570 pins 14/15 and 7.
Set the 2nd gain trim last looking at pins 14 and 15 of the NE570 and setting this trim so that the signal is equal in level to that at pin 7 of the 570. If this can't be done, go as far as the trimmer permits and re-adjust the first gain trim to achieve it.
"
I would use this value, since it will give you unity over the compander.
I guess you could also adjust for unity between IC1_A pin 1 and IC5_B pin 7, both sides of the blend knob, so that you have a perfect blend when the pot is at 12 o'clock.

Another aspect is, if you want the pedal to oscillate at max. feedback. You can adjust gain 2 so that there is oscillation, or not. Your choice.